1. Field of the Invention
The present invention relates to an image forming apparatus for forming an image on a recording material, such as a copying machine, a printer, and a facsimile.
2. Related Background Art
FIGS. 7 and 8 show a construction of a laser beam printer 100 as an example of an image forming apparatus employing an electrophotographic process or other such recording process.
In a laser beam printer, a convey path R is generally set substantially horizontally as shown in FIG. 7, or obliquely as shown in FIG. 8. The convey path R begins at the position of recording material supplying means, which includes a tray on which a recording materials such plain paper can be stacked, and a roller for feeding the recording material into the laser printer from the tray; the recording material in the convey path R is conveyed by way of transferring means for transferring a developed image to the recording material, before reaching fixing means for fixing the developed image on the recording material by heating.
In the laser beam printer 100, a sheet feeding tray 1 and a sheet feeding roller 2 are arranged on one end side (the right-end side in FIGS. 7 and 8) of the convey path R, and a transferring roller 9 is arranged substantially in the middle of the convey path R, with a fixing device 11 as fixing means arranged on the other end side (the left-end side in FIGS. 7 and 8) of the convey path R. Those members are arranged in a substantially straight line, and image forming means such as a process cartridge 7 and optical means such as a laser scanner 5 are arranged above the convey path R.
The feeding of a recording material P, transferring of a developed image (toner image) to the recording material P, and fixing of the developed image on the recording material P are successively performed by those respective means. Then, the recording material P is conveyed by way of a discharge roller pair 12 with its printing surface facing down, to reach a discharge tray 14.
The fixing device 11 and the laser scanner 5 described above are fixed to a main frame F shown in FIGS. 9 and 10 which functions as a frame member.
The main frame F shown in FIG. 9 is made of resin, in which left and right side walls f1 and f2, and connecting portions f3 and f4 connecting the two side walls to each other, are formed through integral molding. The connecting portion f4, which is obliquely set, functions as the convey path R.
Further, the main frame F shown in FIG. 10 has left and right side plates F1 and F2, and connecting members F3, F4, and F5 connecting the two side plates to each other. Those members F1 to F5 are joined together to form the main frame F. In this case as well, the obliquely set connecting member F4 is endowed with a function as the convey path R.
The side plates F1 and F2, and the connecting member F3 and F5 are each made of sheet metal, whereas the connecting member F4 is made of insulating resin. This is because the connecting member F4 is implemented as a portion supporting the transferring means 9 mentioned above. That is, to prevent leakage of a transfer bias, it is preferable to use an insulating resin having an electrical insulating property for such a connecting member F4.
Incidentally, the main frame F forms the frame structure of the laser beam printer, and thus has a size not very different from that of the main body. Accordingly, when, as described in FIG. 9, the main frame F is to be formed of resin through integral molding, not only is a large-sized molding machine necessary, it takes time to fill a molten resin, which serves as a forming material, into the mold, and also to cool the filled molten resin.
Further, numerous limitations apply in the molding of the main frame F due to the shapes of its components, which makes the degree of freedom of design rather low.
In addition, as the configuration of the main frame becomes complex, not only does it take a long time to prepare a forming mold for the main frame, it also drives up cost. Further, there is also the problem of the maintenance of such a forming mold.
In this regard, the above-mentioned problems can be overcome when the main frame F is formed by joining mainly sheet metal members such as those described in FIG. 10.
However, as can be seen in FIG. 10, the connecting member F4 is situated between the connecting members F3 and F5 as seen in the vertical direction, and fixed in place while sandwiched between the left and right side plates F1 and F2 in this state. Accordingly, when maintenance or repair is to be performed on parts mounted to the connecting member F4, it is rather difficult to take out the connecting member F4 from the main frame F, resulting in poor workability.
Further, to perform maintenance or repair on the parts mounted to the connecting member F4, it is necessary to remove the connecting member F3, for example. In this regard, the connecting member F4 and the connecting member F3 are mounted at right angles with respect to the respective main surfaces of the side plates F1 and F2 to which they are mounted, with their weights being balanced in this state with those of the components mounted to the main frame F. Accordingly, when the connecting members F3 and F4 are removed, such a balance is destroyed, causing a reduction in the mechanical strength of the apparatus. Therefore, the apparatus may actually deform when applied with some external force during the maintenance or repair.
Further, when there is a large distance between the fixing device 11 and the discharge tray 14, it is necessary to provide a discharge/convey guide 15 for conveying the recording material from the fixing device 11 to the discharge tray 14, leading to such problems as the increased number of parts, enlarged size of the apparatus, and increased discharge time for the recording material.